Effect of Implementation of Cardiopulmonary Resuscitation-Targeted Multi-Tier Response System on Outcomes After Out-of-Hospital Cardiac Arrest: A Before-and-After Population-Based Study.

A multi-tiered response (MTR) system has been controversial in terms of cost-effectiveness and outcome improvement. It remains uncertain whether a cardiopulmonary resuscitation (CPR)-targeted tiered response system is associated with better outcomes after out-of-hospital cardiac arrest (OHCA). This study aimed to investigate the effect of an MTR on OHCA outcomes. A natural experimental study was conducted for resuscitation-attempted adult OHCAs. The MTR system was implemented in Korea by the National Fire Agency in 2015 across the country where the single-tiered ambulance response system existed. The MTR program had the following 3 components: 1) detection of OHCA by dispatcher, 2) dispatch of ambulance or fire engine in addition to routine dispatch of ambulance, and 3) performance of team CPR. The study period of 2015-2016 was divided by 6 months (phases I [reference], II, III, and IV). The endpoints were prehospital defibrillation, prehospital return of spontaneous circulation (PROSC), survival to discharge and good neurological recovery. A multivariable logistic regression analysis was performed to evaluate the effect of the intervention, and adjusted odds ratios (AORs) with 95% confidence intervals (CIs) were calculated, adjusting for potential confounders. A total of 32,663 eligible OHCA cases were evaluated during the study period. As the intervention program spread, the MTR with ambulance increased (from 7.0% in phase I to 53.7% in phase IV, for trend < 0.01). During the study period, prehospital defibrillation increased from 23.6% in phase I to 26.9% in phase IV and the study outcome was improved from 7.4 to 12.6% for PROSC, from 6.7 to 9.1% for survival to discharge, and from 4.5 to 5.8% for good neurological outcome ( for trend < 0.01 for all). Compared with phase I, the AORs (95% CI) of phase IV were 1.16 (1.08-1.25) for prehospital defibrillation, 1.82 (1.63-2.04) for PROSC, 1.37 (1.21-1.56) for survival to discharge, and 1.23 (1.06-1.43) for good neurological outcome. The nationwide implementation of a multi-tiered response system for OHCA was associated with increased prehospital defibrillation and improved outcomes of OHCA patients.